United States Department of Agriculture-Agricultural Research Service, San Joaquin Valley Agricultural Sciences Center, 9611 South Riverbend Avenue, Parlier, CA 93648-9757, U.S.A.
Citrus Pest Detection Program, Central California Tristeza Eradication Agency, 22847 Road 140, Tulare, CA 93274-9367, U.S.A.
Plant Dis. 2020 Jul;104(7):1925-1931. doi: 10.1094/PDIS-08-19-1791-RE. Epub 2020 May 12.
In California, citrus tristeza virus (CTV) is regulated by a State Interior Quarantine. In CTV abatement districts in central California, trees with CTV that react to MCA13 (MCA13-positive [MCA13+]), a strain-discriminating monoclonal antibody, are rogued to prevent virus spread. The Tulare County Pest Control District, however, does not participate in this abatement program except for a 1.6-km zone around the Lindcove Research and Extension Center, Exeter, CA. To quantify CTV spread under these two disparate management programs, CTV surveys were conducted in abatement plots with mandatory aphid control and nonabatement plots. Abatement plot surveys used hierarchical sampling of 25% of trees with samples pooled from four adjacent trees. Detection of MCA13+ CTV in a sample prompted resampling and testing of individual trees. From 2008 to 2018, incidence of CTV increased by an average of 3.9%, with only two MCA13+ samples detected. In contrast, in nonabatement plots, incidence of CTV increased by an average of 4.6% between 2015 and 2018. Increase in MCA13-negative (MCA-) isolates was 11 times greater than that of MCA13+ isolates, with the number of MCA13+ trees increasing by 19 trees between 2015 and 2018. MCA13- isolates were more randomly distributed, suggesting primary spread, whereas MCA13+ CTV isolates were more aggregated, suggesting some secondary spread. These results suggest that spread of MCA13+ isolates was limited by a combination of tree removal and aphid vector suppression. MCA13+ samples were VT isolates with some mixtures with T30 isolates. Despite the presence of VT isolates, all CTV-infected trees were asymptomatic.
在加利福尼亚州，柑橘衰退病毒（CTV）受到州内检疫的监管。在加利福尼亚州中部的 CTV 防治区，对反应 MCA13（MCA13 阳性 [MCA13+]）的、带有 CTV 的树木进行砍伐，以防止病毒传播。然而，图莱里县害虫防治区除了在林德科夫研究与推广中心（埃克塞特，加利福尼亚州）周围 1.6 公里的区域外，不参与该防治计划。为了在这两种不同的管理计划下量化 CTV 的传播，在强制性防治蚜虫的防治区和非防治区进行了 CTV 调查。在防治区的调查中，使用了从四个相邻树木中采集样本的 25%的树木的分层抽样。在样本中检测到 MCA13+CTV 会促使对单个树木进行重新采样和测试。2008 年至 2018 年期间，CTV 的发病率平均增加了 3.9%，仅检测到两个 MCA13+样本。相比之下，在非防治区，2015 年至 2018 年间，CTV 的发病率平均增加了 4.6%。MCA13-（MCA-）分离株的增加速度比 MCA13+分离株快 11 倍，2015 年至 2018 年间，MCA13+树的数量增加了 19 棵。MCA13-分离株的分布更加随机，表明主要传播，而 MCA13+CTV 分离株的分布更加聚集，表明存在一些二次传播。这些结果表明，MCA13+分离株的传播受到树木砍伐和蚜虫载体抑制的共同作用限制。MCA13+样本是 VT 分离株，有些与 T30 分离株混合。尽管存在 VT 分离株，但所有感染 CTV 的树木均无症状。
